African borders are often a tangle of razor wire, with soldiers at crossing points checking papers, waving on those with valid IDs and turning back the rest.

Even so, an estimated 1,200 undocumented migrants every night cross the Limpopo River, South Africa’s equivalent of the Rio Grande separating the U.S. and Mexico. Most are from Zimbabwe, where shortages of food and fuel and an unemployment rate of more than 80% have sparked a steady exodus to the more stable and more prosperous South Africa.

A milewide “dead zone” fenced on both sides stretches east and west from Beit Bridge, the sole legal crossing between the two countries. Police and military are on patrol day and night.

Some of those caught say they are beaten and sent back. Others pay bribes and go on to Johannesburg, the financial hub of South Africa and a city whose economy is larger than the whole of Zimbabwe‘s.

The beefed-up border is a startling sight for a continent where such barriers not long ago were the rare exception rather than the norm.

Human rights groups say borders across the continent are becoming harder to cross, with guns, dogs and government policies determined not just to keep out illegal crossers, but also to return those who still have no status after entering up to a decade ago.

This year, Angola has deported an estimated 330,000 “irregular migrants” who have fled ethnic violence in neighboring Congo. {snip}

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Equatorial Guinea sparked a diplomatic crisis this month with its neighbor Cameroon after announcing plans to build a wall between the two countries. The former Spanish colony — Africa’s fourth-largest oil producer — says Cameroon allows Nigerians and others to transit its territory and cross the border in search of work.

Freedom House ranks both countries among the world’s least democratic nations. {snip}

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Politics and immigration

In this case, a separatist movement has made the drift of migrants worse. In 1961, two colonies, one British and the other French, were joined to create what is now the Republic of Cameroon, but the English-speaking minority claims it is the target of discrimination and abuse and has long sought to break away as the “Republic of Ambazonia.” The people say they are ethnically closer to the tribes of eastern Nigeria.

Secessionist rallies in recent months led to a crackdown, with troops burning homes and firing on civilians, many of whom fled to neighboring states.

But Gen. Rene Claude Meka, Cameroon’s army chief of staff, called plans for a border wall an act of aggression. In July, he toured the 110-mile border and insisted the project would “not be tolerated.”

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But whether crossing into Cameroon, Zambia, Kenya or Mozambique, there are signs of a new order: more troops, more border checkpoints, more people told they can no longer pass lines drawn in colonial times that divide tribes, ethnic groups and traditional communities.

Police in Johannesburg in the past month have taken to sealing off streets in poor areas, typically at rush hour, blocking doorways and then searching cars and frisking pedestrians. Anyone without a South African identity book or a refugee permit is detained.

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Zimbabweans face a number of physical barriers escaping their country’s woes. Botswana has erected a 310-mile-long, 6-foot-high electrical fence, purportedly to keep out smuggled Zimbabwean cattle that could spread foot-and-mouth disease. South Africa maintains an electrified fence along parts of its border with Zimbabwe and Mozambique.

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“It’s not that you can’t cross without papers, but when controls are tightened, the price of a bribe goes up. Many can no longer afford it.”